1. Field of the Invention
This invention relates generally to the field of flexible circuits, and more particularly to employing flexible circuits to monitor structural health where the structure is subjected to a harsh environment.
2. Description of Related Art
Flexible circuits are circuits designed from very thin layers of flexible metals and other compositions, where the layers include conductive and non-conductive portions creating electrical circuits. As the name implies, flexible circuits are capable of being flexed, and as such flexible circuits can be employed in a variety of applications where a conventional rigid circuit would not be suitable. For example, flexible circuits can be mounted to surfaces having three dimensional curvatures. These flexible circuits are easily mounted to curved surfaces through the use of common adhesives such as epoxy. Such features make flexible circuits ideally suited to monitoring the structural health of a surface of a structure.
A structure, such as an aircraft or bridge, encounters a variety of influences during their service life that can affect the integrity of that structure. Heat and cold can change the properties of metals, and vibrations, strain and loading can induce fatigue stress cracks. Normally, such defects would have to be detected during service operations. However, because many defects may exist without being visible, service inspections do not provide the most reliable means for detecting defects. And although devices exist that can detect these minute defects, such devices typically require lengthy out-of-service intervals while the monitoring devices are deployed over the structure and necessary laboratory-like circumstances are enforced. Moreover, these monitoring devices, such as x-rays, may not be able to be placed in the confined areas of the structure desired to be monitored. Therefore, flexible circuits provide a distinct advantage over other monitoring techniques because they can be placed at practically any point on the structure.
However, because flexible circuits are designed to be mounted to the structure, the flexible circuits are subjected to the same harsh environment to which the structure is subjected. This is disadvantageous, because flexible circuits often contain fragile electronic components not rugged enough to survive in harsh environments. Thus, any advantage gained by deploying flexible monitoring circuits over a structure can be lost if the flexible circuit fails while in-service due to having been exposed to an overly harsh environment. Therefore, it would be advantageous to provide for a flexible circuit which can be employed for structural health monitoring without being susceptible to failure due to being exposed to harsh environments.